How to Grow Plants Indoors Using the Color Spectrum of Light

As a horticulturalist and landscaper it is easy to get caught up in the big picture but it is the fine details that make it so interesting.

Photosynthesis is a process used by plants and other organisms to absorb and convert light energy from the sun or another light source, into chemical energy that can be later released to fuel the organism. In the color spectrum of light, plants use some light waves and reflect others. Plants absorb blue and red light. Blue light induces vegetative growth and red induces flowering. Different plants use different amounts of blue and red, which may be why some plants prefer shade, which provides less red light.

Intensity

Light intensity is the rate at which light spreads over a surface of an area some distance from a source. Light source and distance plays a role in its intensity. Different lights fall in different places on the color spectrum which is why we must be selective with the type of lighting we use and for what purpose. Have you ever seen a Crape Myrtle (sun loving plant) planted in the shade? They will grow taller and thinner due to having to reach for light. Its leaves become bigger, creating more surface area for catching light. It also creates fewer leaves to arrange them to catch sun and not shade itself. This is why it is critical for plants to get the required light intensity to stay healthy.

Color Spectrum

As we discussed the different responses that take place with different color light waves or color temperatures, we need to discuss what lights produce these color temperatures to help us achieve our objective. The color temperature is measured in degrees kelvin. Colors on the blue side of the spectrum are considered cool colors (above 5000k). Colors on the red side of the spectrum are considered warm (below 3000k)

Fluorescent bulbs are efficient, inexpensive to operate and produce little heat which allows the light to be close to the plant without baking it or drying it out. It produces plenty of blue light, therefore works well with foliage. For flowering plants you may need to supplement some warm light with a High Pressure Sodium bulb.

High Pressure Sodium works better in conjunction with other lighting as a supplement for blooming plants to provide extra red light waves. These bulbs produce in the warm red side of the spectrum. These bulbs are efficient but used as a primary light source can prove fatal for many plants due to its lack of range with other colors on the color spectrum.

Metal Halide bulbs produce on the cool blue side of the spectrum and come closest to natural sunlight and are great with foliage production. These bulbs are very inefficiently and fixtures are very expensive.

LED lighting (Light Emitting Diodes) is the latest and greatest and will remain that way for good reason. If you know a plants exact requirements then an LED system can almost be programmed like a computer because they can produce whatever color wavelength desired and only that wavelength. If you want only blue light then you can do that. If you want red only, then that too is doable. These systems are very precise; therefore you will pay a hefty price for them. Because LED lighting can be engineered to whatever color needed, it can fall anywhere on the chart below.

Duration

Have you ever planted your vegetable garden only to not get the results you were looking for? If your garden is not getting the 6 or more hours of full sun it needs then there will be a breakdown in photosynthesis which will send your plants into survival mode. This simply means no blooming or fruit production. It is no different with indoor plants either.

Perhaps your indoor plants are using sunlight from a south facing window. During the summer, daylight hours are much longer and your plants do well. Winter comes and the duration of sunlight becomes much less and your plants may need supplemental light. Getting the right amount of light is not enough if they are not getting it long enough each day.